JP2006523940A - Fuel cell with super water-repellent surface - Google Patents

Abstract

A fuel cell comprising a component having a durable super-water-repellent surface at selected locations where water condensation occurs. A superhydrophobic surface generally has a substrate portion with a plurality of protruding micro- or nano-scale protrusions arranged such that the surface has a predetermined contact line density greater than or equal to the critical contact line density.

Description

RELATED APPLICATIONS This application is a US Provisional Patent Application No. 60 / 462,963, filed Apr. 15, 2003, entitled “Superhydrophobic Surface of High Pressure Liquid”, which is hereby fully incorporated by reference. And U.S. Utility Patent Application No. 10 / 662,679, filed Sep. 15, 2003 and entitled “Fuel Cell with Super-Water-Repellent Surface”, which is incorporated herein by reference in its entirety. Insist on profit.

The present invention relates generally to fuel cells, and more particularly to water treatment of fuel cells.

BACKGROUND OF THE INVENTION Fuel cell technology has been the subject of many recent research and development activities because of environmental and long-term fuel supply considerations associated with engines and burners that burn fossil fuels. Fuel cell technology generally promises a clean energy source that is small and lightweight enough to enable use in vehicles. Moreover, fuel cells are placed near the point of energy use in fixed applications, thus significantly reducing the inefficiencies associated with energy transmission over long distances.

  Although a variety of fuels and materials are used for fuel cells, all fuel cells typically have an anode and an opposing cathode separated by an electrolyte. The anode and cathode are generally porous, with fuel being introduced into the cell from one side, generally the cathode, and the oxide, on the other hand, generally from the anode. The fuel oxidizes in the cell and generates a direct current with water and heat as by-products. Each cell typically generates a potential of about 1 volt, but any number of cells are connected in series and separated by a separator plate to form a fuel cell stack that provides the desired value of potential. Also good. In modern fuel cell designs, the anode, cathode, and electrolyte are often combined to form a membrane electrode assembly, and the separator plate and current collector are combined to form a “bipolar plate”. Details of the design and operation of the fuel cell are further described in Non-Patent Document 1, which is fully incorporated herein by reference. Various fuel cell components, including membrane electrode assemblies and bipolar plates, are further described in US Pat. Each of which is hereby fully incorporated by reference.

  An unchanging problem in the design of fuel cells is the problem of water treatment in the battery. Under certain conditions, water is generated very rapidly in the battery. This water is generally generated on the cathode side of the cell and, if accumulated, restricts or prevents fuel flow into the cell. This situation is known in the industry as “cathode flooding”. Moreover, due to the large temperature difference between the battery and the surrounding environment, water vapor condensation sometimes occurs when air enters and exits the battery during operation.

Generally, the surface of the bipolar plate is provided with a drainage channel, and water is sent to the collection area through the drainage channel and drained from the battery. In addition, since bipolar plates are often manufactured from materials with a relatively low surface energy, draining water from the bipolar plates is relatively easy. However, none of these measures have been fully successful in overcoming the problem of cathode flooding and water treatment in fuel cells. In particular, when low surface energy materials such as PTFE are used in a fuel cell, the water droplets are not drained as desired and adhere to the cell's bipolar plates and other surfaces. What is needed in the industry is a fuel cell with components that facilitate improved drainage in the cell.
US Pat. No. 4,988,583 US Pat. No. 5,733,678 US Pat. No. 5,798,188 US Pat. No. 5,858,569 US Pat. No. 6,071,635 US Pat. No. 6,251,308 US Pat. No. 6,436,568 US Published Patent Application No. 2002/0155333 US Published Patent Application No. 2003/0108449 "Fuel Cell Handbook 5th Edition" published by the US Department of Energy's National Institute of Energy Technology in Morgantown, West Virginia in October 2000

  The present invention substantially satisfies the needs of the industry described above. The present invention has a fuel cell stack device with components having a durable super-water-repellent surface at selected locations where water condensation occurs and improves drainage in the device. Since the super water-repellent surface has high water repellency, the tendency of water droplets to adhere to the surface is significantly suppressed, thereby significantly improving drainage in the battery.

ここで、Ｐは流体流路内の所定の最高予想流体圧力値、γは液体の表面張力、θ_ａ，０は、実験測定による突出部材料上の液体の度単位の真の前進接触角、ωは度単位の突出部立上り角である。概して、超撥水性表面の撥水性を最適化するため、突出部の間隔寸法に対する突出部の断面寸法の比は０．１以下であることが望ましい。 A superhydrophobic surface generally has a substrate portion with a plurality of micro- or nano-scale protrusions of protruding regular shapes arranged in a regular array, the surface being a critical contact determined by It has a predetermined contact line density obtained by measuring the contact line per square meter of the surface area, which is equal to or greater than the linear density value “Λ _L ”, in meters.

Where P is the predetermined maximum expected fluid pressure value in the fluid flow path, γ is the surface tension of the liquid, θ _{a, 0} is the true advancing contact angle in degrees of liquid on the protrusion material from experimental measurements, ω is the protrusion rising angle in degrees. In general, in order to optimize the water repellency of the super-water-repellent surface, it is desirable that the ratio of the cross-sectional dimension of the protrusion to the distance between the protrusions is 0.1 or less.

  The protrusions are formed in the substrate material itself or on its surface, or in one or more layers of material disposed on the substrate surface. Protrusions are regular or irregularly shaped three-dimensional solids or depressions that are arranged in some regular geometric pattern.

ここで、ｄは隣接する突出部の間のメートル単位の最短距離、θ_ａ，０は、表面における液体の度単位の真の前進接触角、ωは度単位の突出部立上り角である。 Protrusions using photolithography or nanomachining, microstamping, microcontact printing, self-assembly of metal colloid monolayers, atomic force microscopy nanomachining, sol-gel molding, self-assembled monolayer orientation It is formed by sex patterning, chemical etching, sol-gel stamping, colloidal ink printing, or by placing a layer of carbon nanotubes on a substrate. The process further comprises determining a critical protrusion height value “Z _c ” in meters according to the following equation:

Where d is the shortest distance in meters between adjacent protrusions, θ _{a, 0} is the true advancing contact angle in degrees of liquid on the surface, and ω is the rise angle of the protrusion in degrees.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS In this application, the term “fuel cell” means any type of electrochemical fuel cell device, proton exchange membrane fuel cell (PEMFC), alkaline fuel cell (AFC), phosphorus Examples include, but are not limited to, acid fuel cells (PAFC), molten carbonate fuel cells (MCFC), and solid oxide fuel cells (SOFC). The term “fuel cell stack device” refers to a device that includes any and all of at least one fuel cell and its components, along with any and all of the independent components related to the function of the fuel cell, Including, but not limited to, insulators, manifolds, piping, and electrical components.

  A surface that is resistant to wetting by a liquid is referred to as a “repellent” surface. Such a surface is known as water repellency when the liquid is water and is known as liquid repellency with respect to other liquids. If the surface is resistant to wetting to the extent that a microdroplet of water or other liquid exhibits a very high static contact angle (greater than about 120 degrees) to the surface, the surface will retain the droplet A surface is referred to as a “super-water-repellent” or “super-liquid-repellent” surface when the tendency is very low, or when a liquid / gas / solid interface is present on the surface when fully immersed in the liquid. In this application, the term superhydrophobic is generally used to refer to both superhydrophobic and superhydrophobic surfaces.

  It is now well known that surface roughness has a significant effect on the degree of surface wetting. In some situations, roughness has been observed to adhere liquid more firmly to a surface than a corresponding smooth surface. In other situations, however, roughness also results in the liquid not sticking to a rougher surface as hard as a smoother surface. In some situations, the surface is super water repellent. Such superhydrophobic surfaces generally take the form of a substrate member comprising a plurality of micro- to nano-scale protrusions or recesses, referred to herein as “protrusions”.

  A portion of an embodiment of a fuel cell stack apparatus 100 according to the present invention is depicted in simplified cross-section in FIG. The fuel cell stack apparatus 100 generally has a membrane electrode assembly 102 separated by a bipolar plate 104. The end plate 106 has a device 100 at each end. Each membrane electrode assembly 102 generally includes an anode membrane structure 108, a cathode membrane structure 110, and an electrolyte 112.

  Bipolar plate 104 and end plate 106 are typically manufactured from a conductive, corrosion-resistant and heat-resistant material, such as a metal or carbon-filled polymer. The surface 114 of the bipolar plate 104 and the inwardly facing surface 116 of the end plate 106 generally have passages 118 for transporting fuel and oxide to the membrane electrode assembly 102 and draining water. The heat transfer portion 120 of the bipolar plate 104 and end plate 106 provides an additional surface area for removing heat from the battery.

  According to the present invention, all or any desired portion of the outer surface of the bipolar plate 104 or end plate 106 is a super water-repellent surface. For example, as depicted in FIG. 1 b, a super water-repellent surface 20 is provided on the inward surface 121 of the passage 118 to improve drainage in the passage 118. Water droplets generated in the reaction process are repelled by the super water-repellent surface 20, and the water is drained from the passage 118 by gravity.

  As depicted in FIG. 1a, other portions of the bipolar plate 104 or end plate 106, such as the heat transfer portion 120 and the outer surface 122, are also provided with super-water-repellent surfaces 20 to collect on these surfaces or The drainage of condensed water may be improved. Other parts of the fuel cell stack assembly, such as fuel and oxide manifolds and piping (not shown), vents (not shown), and vessel surfaces (not shown) are also provided with a super-water-repellent surface 20 to provide an ambient environment. Water that condenses on these parts may be discharged by the movement of wet gas between the battery and the elevated temperature in the battery. It will be readily appreciated that the super water-repellent surface 20 according to the present invention is provided in any desired portion of any fuel cell stack device component to improve its drainage characteristics.

  A greatly enlarged view of a super water-repellent surface 20 according to the present invention is depicted in FIG. The surface 20 generally has a substrate 22 with a number of protrusions 24. Each protrusion 24 includes a plurality of side surfaces 26 and an upper surface 28. Each protrusion 24 has a width dimension labeled “x” in the figure and a height dimension labeled “z” in the figure.

  As depicted in FIGS. 1-3, the protrusions 24 are arranged in a regular rectangular array, and each protrusion is spaced from adjacent protrusions by a spacing dimension indicated by “y” in the figure. . The angle defined by the upper surface edge 30 of the protrusion 24 is indicated by φ, and the rising angle of the side surface 26 of the protrusion 24 with respect to the substrate 22 is indicated by ω. The sum of the angles φ and ω is 180 degrees.

  The super water repellent surface 20 generally exhibits super water repellency when a liquid / solid / gas interface is maintained on the surface. As depicted in FIG. 7, when the liquid 32 contacts only the top surface 28 and a portion of the side surface 26 proximate the top edge 30 of the protrusion 24, the space 34 between the protrusions has air in the space 34. Or it remains filled with other gases and the necessary liquid / solid / gas interface is present. It can be said that the liquid is “suspended” between the upper surface of the protrusion 24 and the upper edge 30.

  As disclosed below, the formation of the liquid-solid-gas interface depends on the predetermined correlated geometric parameters of the protrusion 24 and the nature of the liquid and the interaction of the liquid and the solid surface. According to the present invention, the geometric parameters of the protrusions 24 are selected so that the surface 20 exhibits super water repellency at the desired hydraulic pressure.

ここで、ｙはメートル単位で測定された突出部間の間隔である。 With reference to the rectangular array of FIGS. 1-3, the surface 20 is divided into uniform areas 36 surrounding each protrusion 24, drawn with dotted lines as boundaries. The surface density (δ) of the protrusions in each uniform area 36 is expressed by the following equation.

Here, y is the distance between the protrusions measured in meters.

であり、ここで、ｘはメートル単位の突出部の幅である。 1-3, the circumferential length (p) of the upper surface 28 at the upper edge 30 is as follows.

Where x is the width of the protrusion in meters.

となる。 The circumference p is called the “contact line” that defines the location of the liquid / solid / gas interface. The surface contact line density (Λ), that is, the length of the contact line per unit area of the surface, is the product of the circumference (p) and the surface density (δ) of the protrusions.

It becomes.

となる。 For a rectangular array of rectangular protrusions depicted in FIGS.

It becomes.

ここで、（ｐ）は液体の密度、（ｇ）は重力による加速度、（ｈ）は液体の深さである。ゆえに、例えばおよそ１０００ｋｇ／ｍ^３の密度を持つ１０メートルの水柱では、体積力（Ｆ）は

となる。 When the body force (F) due to gravity acting on the liquid is smaller than the surface force (f) acting on the contact line of the protrusion, a certain amount of liquid is suspended on the protrusion 24. The body force (F) related to gravity is determined by the following equation.

Here, (p) is the density of the liquid, (g) is the acceleration due to gravity, and (h) is the depth of the liquid. Thus, for example, for a 10 meter water column with a density of approximately 1000 kg / m ³ , the body force (F) is

It becomes.

となる。 On the other hand, the surface force (f) is the surface tension (γ) of the liquid, the apparent contact angle θ _s of the side surface 26 of the protrusion 24 with respect to the normal, the contact line density (Λ) of the protrusion, and the apparent contact area of the liquid. (Α) depends on

It becomes.

The true advancing contact angle (θ _{a, 0} ) of the liquid on a given solid material is defined as the maximum experimentally measured static contact angle of the liquid on the material surface with essentially no protrusions. The true advancing contact angle can be easily measured by techniques well known in the art.

Suspended drops on the surface with protrusions show true advancing contact angle values (θ _{a, 0} ) on both sides of the protrusions. The contact angle (θ _s ) with respect to the normal on the side surface of the protrusion is related to the true advancing contact angle (θ _{a, 0} ) by φ or ω as follows.

ここで、ｇは液体の密度（ρ）、（ｇ）は重力による加速度、（ｈ）は液体の深さ、液体の表面張力（γ）、ωは基板に対する突出部の側面の度単位の立上り角、および（θ_ａ，０）は実験測定による突出部材料上の液体の度単位の真の前進接触角である。 By obtaining the contact line density Λ by making F and f equal, the critical contact line density parameter Λ _L is determined as follows in order to predict the super-water repellency at the surface.

Where g is the density (ρ) of the liquid, (g) is the acceleration due to gravity, (h) is the depth of the liquid, surface tension (γ) of the liquid, and ω is the rise in degrees on the side surface of the protrusion relative to the substrate. The angle, and (θ _{a, 0} ) is the true advancing contact angle in degrees of liquid on the protrusion material from experimental measurements.

When Λ> Λ _L , the liquid is suspended on the protrusion 24 to form a super water-repellent surface. When Λ <Λ _L , the liquid falls from the protruding portion, and the contact interface on the surface becomes a simple liquid / solid having no super-water-repellency.

ここで、Ｐは表面が超撥水性を必ず示すキログラム／平方メートル単位の最大圧力、γは液体のニュートン／メートル単位の表面張力、θ_ａ，０は実験測定による突出部材料上の液体の度単位の真の前進接触角、およびωは度単位の突出部立上り角である。 It will be appreciated that by substituting appropriate values for the numerators in the above equation, the critical contact line density value is determined to design a surface that retains super water repellency at the desired amount of pressure. . The equations are generalized as follows:

Where P is the maximum pressure in kilograms / square meter that the surface must exhibit super water repellency, γ is the surface tension in liquid Newtons / meter, and θ _{a, 0} is the degree unit of the liquid on the protrusion material from experimental measurements. Is the true advancing contact angle, and ω is the protrusion rise angle in degrees.

  It is generally expected that the surface 20 formed according to the above relationship will exhibit super water repellency at hydraulic values up to and including the value of P used in equation (9) above. Super water repellency is exhibited whether the surface is immersed, subjected to a liquid jet or spray, or struck by individual droplets.

  Once the critical contact line density value is determined, the remaining details of the protrusion geometry are determined according to the relationship between x and y given by the equation for contact line density. In other words, the surface geometry is determined by selecting any value of x or y in the contact line equation and determining other variables.

ここで、（λ_ｐ）は突出部沿いの接触直線比（linearfraction）、（△θ_０）は表面材料について真の前進接触角（θ_ａ，０）と真の後退接触角（θ_γ，０）との差、および（ω）は突出部の立上り角である。正方形突出部の長方形アレイに対しては、

となる。 The tendency of the super water-repellent surface 20 to repel the droplet and the droplet to contact the surface at a very high contact angle is the contact angle hysteresis (Δθ) which is the difference between the advancing contact angle and the receding contact angle of the droplet on the surface. ) Is best represented. In general, a low contact angle hysteresis value corresponds to a relatively high surface water repellency. Surface contact angle hysteresis is determined by the following equation:

Where (λ _p ) is the contact linear ratio along the protrusion (linear fraction), and (Δθ ₀ ) is the true advancing contact angle (θ _{a, 0} ) and true receding contact angle (θ _{γ, 0} ) for the surface material. ) And (ω) are the rising angles of the protrusions. For a rectangular array of square protrusions,

It becomes.

また、実際の後退接触角は以下の等式によって決定される。

An equation for determining (λ _p ) for surfaces having other geometric shapes is given in FIG. For droplets on the surface, the actual advancing contact angle of the surface is determined by the following equation:

The actual receding contact angle is determined by the following equation.

By examining the above relationship, a relatively low value of λ _p , ω, x / y, Λ results in a relatively improved surface water repellency and a relatively high value for each of these same parameters. It will be readily understood that the ability to suspend the liquid column is relatively improved. Therefore, if a surface with good water repellency and suspension properties is desired, it is generally necessary to balance the values of these parameters.

  The above equation is also used to plot a given liquid property relationship between protrusion spacing (y) and maximum pressure (P) for various x / y values. Such a plot, an example of which is shown in FIG. 17, serves as a useful design tool as demonstrated in the example given below.

ここで、（ｄ）は接触線における隣接する突出部の間の最短距離、ωは突出部立上り角、θ_ａ，０は実験測定による突出部材料上の液体の真の前進接触角である。突出部（２４）の高さ（ｚ）は、臨界突出部高さ（Ｚ_ｃ）に少なくとも等しいか、望ましくはこれより高い。 As depicted in FIG. 6, the liquid interface deflects downward by an amount D ₁ between adjacent protrusions. If the amount D ₁ is greater than the height (z) of the protrusion 24, the liquid contacts the substrate 22 at a point between the protrusions 24. When this occurs, the liquid is attracted to the space 34 and falls from the protruding portion, and the super-water repellency of the surface is impaired. The value of D ₁ represents the critical protrusion height (Z _c ) and can be determined by the following equation.

Here, (d) is the shortest distance between adjacent protrusions in the contact line, ω is the protrusion rising angle, and θ _{a, 0} is the true advancing contact angle of the liquid on the protrusion material by experimental measurement. The height (z) of the protrusion (24) is at least equal to, or preferably higher than, the critical protrusion height (Z _c ).

  1-3, the protrusion rise angle ω is 90 degrees, but other protrusion geometries are possible. For example, ω may be an acute angle as depicted in FIG. 9 or an obtuse angle as depicted in FIG. In general, ω is preferably between 80 and 130 degrees.

  It will also be appreciated that a variety of protrusion shapes and arrangements are possible within the scope of the present invention. For example, the protrusion may be a polyhedron, a cylinder depicted in FIGS. 11-12, a similar cylinder, or other suitable three-dimensional shape. The protrusions may be randomly distributed as long as the critical contact line density is maintained, but such a random configuration is less desirable due to the low predictability of super-water repellency. In such a random configuration of protrusions, the critical contact line density and other related parameters can be conceptualized as the average value of the surface. The table in FIG. 13 lists formulas for calculating contact line density for various other protrusion shapes and arrangements.

  In addition, various strategies can be used to optimize the contact line density of the protrusions. As depicted in FIGS. 14 and 15, the protrusion 24 may be formed with a base 38 and a head 40. As the circumference of the head 40 at the upper surface edge 30 becomes longer, the surface contact line density becomes higher. In addition, as illustrated in FIG. 16, the contact line density may be increased by forming a feature such as the depression 42 in the protruding portion 24 and increasing the circumference at the upper surface edge 30. The protrusion may be a recess formed in the substrate.

The protrusions may comprise a rectangular array as described above, a polygonal array such as the hexagonal array depicted in FIGS. 4-5, or a circular or oval array.
The protrusions may be randomly distributed as long as the critical contact line density is maintained, but such a random configuration is less desirable due to the low predictability of super-water repellency. In such a random configuration of protrusions, the critical contact line density and other related parameters can be conceptualized as the average value of the surface. The table in FIG. 13 lists formulas for calculating contact line density for various other protrusion shapes and arrangements.

  In general, the substrate material may be a material in which micro- or nano-scale protrusions are appropriately formed. The protrusions are formed directly on the substrate material itself or one or more other materials deposited on the substrate material, either by photolithography or various suitable methods. Direct extrusion is used to form protrusions in the form of parallel ridges. Such parallel ridges are most preferably oriented in a direction transverse to the direction of fluid flow. A photolithography method suitable for the formation of micro / nanoscale protrusions is disclosed in PCT Published Patent Application No. WO 02/084340, which is fully incorporated herein by reference.

  Other methods suitable for forming protrusions of desired shape and spacing are the nanomachining disclosed in US 2002/00334879, the micro-dissociation disclosed in US Pat. No. 5,725,788. Stamping, microcontact printing method disclosed in US Pat. No. 5,900,160, self-assembly of metal colloid monolayer disclosed in US Pat. No. 5,609,907, US Pat. No. 6,444,444 Micro stamping disclosed in US Pat. No. 254, atomic force microscope nanomachining disclosed in US Pat. No. 5,252,835, nanomachining disclosed in US Pat. No. 6,403,388, US Pat. Sol-gel molding disclosed in US Pat. No. 530,554, surface self-assembled monolayer disclosed in US Pat. No. 6,518,168 Including directional patterning, chemical etching disclosed in US Pat. No. 6,541,389, or sol-gel stamping disclosed in US Published Patent Application No. 2003/0047822, all of which are fully incorporated herein. Is incorporated by reference. Carbon nanotube structures can also be used to form the desired protrusion shape. Examples of carbon nanotube structures are disclosed in US Published Patent Application Nos. 2002/0098135 and 2002/0136683, which are also fully incorporated herein by reference. Moreover, a suitable protrusion structure is formed by using well-known printing with colloidal ink.

  In some applications, particularly when the component is not subjected to high pressure, the super-water-repellent surface 20 is formed by a coating of polymeric material applied using well-known chemical vapor deposition techniques or chemical surface modification techniques. For example, a thin layer of low surface energy material is formed on the surface of the component using gas phase polymerization. In this application, low surface energy materials are generally materials having a surface energy value of less than about 35 mN / m. The resulting superhydrophobic surface 20 is generally characterized by protrusions randomly formed and arranged in a low surface energy material. Alternatively, the surface of the part may be subjected to a chemical surface modification process such as low temperature oxygen plasma or corona discharge treatment. In short, any process capable of producing a random shape and array of protrusions with the desired contact line density is used and is considered to be within the scope of the present invention.

  In another embodiment for low pressure applications, a fractal superhydrophobic surface is formed as a material layer on the substrate. In one such embodiment, a layer of alkyl ketone dimer (AKD) or similar material is melted or injected into a polymer substrate and cured in a nitrogen gas atmosphere. One suitable method for forming an AKD surface is described in T. P. 2125 in a paper entitled “Superhydrophobic Fractal Surface” (Langmuir Vol. 12, No. 9, May 1, 1996). Onda, et al. And this paper is fully incorporated herein by reference.

  In another embodiment suitable for low fluid pressure applications, a polymeric material such as polypropylene is dissolved in a solvent such as p-xylene. A predetermined amount of non-solvent, such as methyl ethyl ketone, is added to the solution and the solution is deposited on the component substrate. When the solvent evaporates, a porous gel-like superhydrophobic surface structure results.

  In each of the polymer layers described above, the resulting surface is generally characterized by protrusions of random shape and configuration. The actual contact critical density and critical contact linear density values for such surfaces are difficult to determine due to variations in individual protrusions, but these surfaces have surface contact linear density values that are critical surface contact density. If it is equal to or exceeds this, it indicates super water repellency. For such surfaces, the actual linear density will inevitably be the average value of the surface due to the variability of the dimensions and geometry of the individual protrusions. Moreover, the protrusion rising angle ω in the above equation is an average value of the surface. Of course, it will be appreciated that any other method by which micro / nanoscale protrusions can be accurately formed can be used and is considered within the scope of the present invention.

In general, it is most desirable to optimize the water repellency of the super water-repellent surface of the fuel cell component in order to obtain the highest drainage. As already explained, the surface water repellency is optimized by selecting relatively low values for λ _p , ω, x / y, Λ, but at the highest pressure the surface is expected to experience in the cell. It is still ensured that the surface has a critical contact linear density value (Λ _L ) sufficient to ensure that it has super water repellency. For best water repellency, the x / y ratio of the protrusion shape should be less than about 0.1, most preferably about 0.01.

  One such method for optimizing the super water-repellent surface of a fuel cell stack device component for water repellency is illustrated by the following example.

Example:
Assume that a super water-repellent surface is provided on the fuel cell bipolar plate. Assume that the highest expected operating pressure in the fuel cell stack assembly is 5 atmospheres and that the bipolar plate material has the following characteristics:

および、

となる。 The super water-repellent surface has a square column (ω = 90 °) array on a bipolar plate. The water repellency of the super water repellent surface is optimized by selecting the following small x / y ratio to increase the actual advancing and receding contact angles of water at the fluid contact surface.
Select x / y = λ _p = 0.1.
therefore,

and,

It becomes.

次に、Ｚ_ｃを求めると以下のようになる。

The liquid is water and the values of θ _{a, 0} and θ _{r, 0} are matched to the material having the above-described characteristics, so that the protrusion spacing (y) and maximum pressure (P) for various x / y values Referring to FIG. 17 plotting the relationship, it can be seen that when the maximum pressure is 51,500 Pa and the x / y ratio is 0.1, y should be about 5 × 10 ⁻⁷ m or 0.5 μm. Therefore, it becomes as follows.

Then, as it follows and seek Z _c.

  Thus, when square protrusions are provided on a bipolar plate in a rectangular array, the cross-sectional dimension is about 50 nm, about 0.5 μm apart, and the height is at least 80 nm.

  It will be readily apparent that the above procedure can be used for any protrusion spacing and geometry desired, as well as any desired surface material and geometry.

  Due to the tendency of the surface to suspend and repel droplets and roll the droplets freely by gravity in the direction of the surface inclination, it is expected that fuel cell parts with super water-repellent surfaces will show greatly improved drainage. The The super water-repellent surface is durable and can exhibit super water repellency at pressures up to the design pressure selected by the method described above. Moreover, the super water-repellent surface according to the present invention is expected to improve the heat shielding from the surface due to the increased surface area of the protrusions on the surface.

  Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art upon consideration of the following or may be learned by practice of the invention. right. The objects and advantages of the invention will be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

1 is a very enlarged perspective view of a super water-repellent surface according to the present invention, with a plurality of nano / micro scale protrusions arranged in a rectangular array. 1 is a simple cross-sectional view of a fuel cell stack device having a super water-repellent surface according to the present invention. FIG. 2 is a partially enlarged view of the fuel cell stack apparatus of FIG. 1 a showing one passage of the apparatus. It is a top view which shows a part of surface of FIG. FIG. 3 is a side view of the surface portion shown in FIG. 2. FIG. 6 is a partial plan view showing an alternative embodiment of the super water-repellent surface according to the present invention, wherein the protrusions are arranged in a hexagonal array. FIG. 5 is a side view of the alternative embodiment of FIG. 4. It is a side view which shows the bending of the liquid suspended between protrusion parts. It is a side view which shows the fixed amount of liquid suspended on the protrusion part. It is a side view which shows the liquid which contacts the bottom face of the space between protrusion parts. FIG. 6 is a side view of a single protrusion in an alternative embodiment of a super water-repellent surface according to the present invention, where the protrusion rise angle is an acute angle. FIG. 6 is a side view of a single protrusion in an alternative embodiment of a super water-repellent surface according to the present invention, where the protrusion rising angle is obtuse. FIG. 4 is a partial plan view of an alternative embodiment of a super water-repellent surface according to the present invention, wherein the protrusions are cylindrical and arranged in a rectangular array. FIG. 12 is a side view of the alternative embodiment of FIG. 11. 6 is a table listing equations for contact line density and linear contact ratio for various protrusion shapes and arrangements. It is a side view which shows the alternative Example of the super water-repellent surface based on this invention. FIG. 15 is a plan view of the alternative embodiment of FIG. 14. FIG. 6 is a plan view showing a single protrusion in an alternative embodiment of a super water-repellent surface according to the present invention. FIG. 6 is a graphical representation showing the relationship between protrusion spacing (y) and maximum pressure (P) for various values of x / y ratio for a particular superhydrophobic surface and liquid.

Claims (32)

Parts of a fuel cell stack device,
A body having a surface portion adapted to repel liquid, the surface portion having a substrate with a plurality of protrusions thereon, each protrusion having a cross-sectional dimension and a protrusion rising angle relative to the substrate; The protrusion is dispersed so that the surface portion has a contact line density value measured in meters of the contact line per square meter of the surface area, which is equal to or greater than the critical contact line density value “Λ _L ” determined by the following equation: ,

Where P is the predetermined maximum expected pressure value at the surface portion, γ is the surface tension of the liquid, θ _{a, 0} is the true advancing contact angle in degrees of liquid on the protrusion material from experimental measurements, and ω is the protrusion Parts of the fuel cell stack device, which is a part rising angle.   The component of claim 1, wherein the protrusions have a substantially uniform shape and dimensions, the protrusions are arranged in a substantially uniform pattern, and the protrusions are spaced apart by a substantially uniform spacing dimension.   The component according to claim 2, wherein a ratio of a cross-sectional dimension of the protrusion to a distance between the protrusions is 0.1 or less.   The component of claim 1, wherein the component is a bipolar plate.   The component of claim 1, wherein the component is a manifold.   The component according to claim 1, wherein the protrusion is a protrusion.   The component according to claim 6, wherein the protrusion has a polyhedral shape.   The component of claim 6, wherein each protrusion has a substantially square cross section.   The component of claim 6, wherein the protrusion is in the shape of a cylinder or a similar cylinder.   2. The component according to claim 1, wherein the protrusion is a recess formed in the substrate. The protrusion has a substantially uniform protrusion height with respect to the substrate, the protrusion height being greater than a critical protrusion height value “Z _c ” in meters determined by the following equation:

Where d is the shortest distance in meters between adjacent protrusions, θ _{a, 0} is the true advancing contact angle in degrees of liquid on the protrusion material from experimental measurements, and ω is in degrees The component of claim 1, wherein the protrusion has a rising angle. A method of manufacturing a component of a fuel cell stack device, the component having a surface portion adapted to repel liquid, the method comprising:
Forming a component body having a surface; and disposing a plurality of protrusions on at least a portion of the surface, each protrusion having a cross-sectional dimension and a protrusion rising angle with respect to the surface. The protrusion is arranged such that the surface has a contact line density measured in meters of a contact line per square meter of surface area that is equal to or greater than a critical contact line density value “Λ _L ” determined by the following equation:

Where P is the predetermined maximum expected pressure value, γ is the surface tension of the liquid, θ _{a, 0} is the true advancing contact angle in degrees of liquid on the protrusion material from experimental measurements, and ω is the rise of the protrusion How to be horns.   The protrusions have a substantially uniform shape, and the step of disposing the protrusions on the surface includes arranging the protrusions in a substantially uniform pattern such that the protrusions are spaced apart by a substantially uniform spacing dimension. 13. The method of claim 12, comprising arranging.   The method according to claim 13, wherein the protrusions are arranged such that a ratio of a cross-sectional dimension of the protrusions to a distance between the protrusions is 0.1 or less.   The method according to claim 13, wherein the protrusions are arranged such that a ratio of a cross-sectional dimension of the protrusions to a distance between the protrusions is 0.01 or less.   14. The method of claim 13, further comprising selecting a geometric shape for the protrusion.   14. The method of claim 13, further comprising selecting an array pattern for the protrusions.   14. The method of claim 13, further comprising selecting at least one dimension for the protrusion and determining at least one other dimension of the protrusion using an equation for contact line density.   The steps of placing protrusions on the surface are nanomachining, microstamping, microcontact printing, self-organized metal colloid monolayer, atomic force microscope nanomachining, sol-gel molding, self-organized monolayer directional patterning, 13. The method of claim 12, comprising forming the protrusions by a process selected from the group consisting of chemical etching, sol-gel stamping, colloidal ink printing, and placing a layer of carbon nanotubes on the surface.   The method of claim 12, wherein the step of disposing the protrusion on the surface comprises forming the protrusion by extrusion. Determining the critical protrusion height value “Z _c ” in metric units according to the following equation:

Where d is the shortest distance in meters between adjacent protrusions, θ _{a, 0} is the true advancing contact angle in degrees of liquid on the surface, and ω is the rise angle of the protrusion in degrees. Item 12. The method according to Item 12. A fuel cell stack apparatus having at least one component having a surface portion adapted to repel liquid, the surface portion having a substrate with a plurality of protrusions thereon, each protrusion having a cross-sectional dimension and a substrate The contact line density value obtained by measuring the contact line per square meter of the surface area in units of meters, wherein the protrusion has a critical contact line density value “Λ _L ” determined by the following formula. The surface portion is dispersed so that it has

Where P is the predetermined maximum expected pressure value at the surface portion, γ is the surface tension of the liquid, θ _{a, 0} is the true advancing contact angle in degrees of liquid on the protrusion material from experimental measurements, and ω is the fuel cell stack device, which is the rising angle of the protrusion.   23. The apparatus of claim 22, wherein the protrusions have a substantially uniform shape and dimensions, the protrusions are arranged in a substantially uniform pattern, and the protrusions are spaced apart by a substantially uniform spacing dimension.   The apparatus of claim 23, wherein the ratio of the cross-sectional dimension of the protrusions to the spacing dimension of the protrusions is 0.1 or less.   The component of claim 22, wherein the component is a bipolar plate.   23. The apparatus of claim 22, wherein the part is a manifold.   23. The apparatus of claim 22, wherein the protrusion is a protrusion.   27. The apparatus of claim 26, wherein the protrusion is in the shape of a polyhedron.   27. The apparatus of claim 26, wherein each protrusion has a generally square cross section.   27. The apparatus of claim 26, wherein the protrusion is in the shape of a cylinder or a similar cylinder.   The apparatus of claim 22, wherein the protrusion is a recess formed in the substrate. The protrusion has a substantially uniform protrusion height with respect to the substrate, and the protrusion height is greater than a critical protrusion height value “Z _c ” determined by the following equation:

Where d is the shortest distance in meters between adjacent protrusions, θ _{a, 0} is the true advancing contact angle in degrees of liquid on the protrusion material from experimental measurements, and ω is in degrees 23. The apparatus of claim 22, wherein the protrusion rise angle.

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